Its easy to get in touch with your Farmbrite contacts is you have an email address associated with their contact record. Just navigate to the Contacts section on the left, and you'll see their email address as a clickable link in your Contacts List. Click it to open your default email program with their email address prepopulated into the recipient field. Write your message and send it off!
If you are already on the Contact Details page, you can also click the Email Envelope icon to initiate the same process.
Note that this will use your computer's default email program to open the email link. If you use Gmail, you can follow these steps from Google to set it as your default program.